Our present invention relates to a drafting frame for a spinning machine of the type in which a plurality of roller pairs draft a roving between them and consist of upper and lower rolls of which the upper rolls are usually mounted on a weighting member and wherein one or more of the rolls or roll pairs can be provided with a belt.
More particularly the invention relates to a drafting frame of this type which is provided with a pneumatic condensing or compacting unit in which the fibers of the roving are drawn together by pneumatic means as they pass along a perforated surface so that within a fiber bundling zone, fibers of the roving which may project outwardly are drawn together or bundled.
A double-belt drafting frame is described in German patent document DE 43 23 472 C2 in which the roving upstream of the output pair of rollers of the drafting frame is engaged by a belt having a perforation and guided along suction shoes so that the fibers are bundled together into a thread. Over the output roller pair of the drafting frame a suction air stream is passed transversely to the transport direction over the length of the fiber bundling zone.
Another condensing or compaction system for a roving is shown in German patent document DE 198 46 268 A1. In this arrangement the drafting frame has at its output side a clamping roller which is driven by one of the output rollers of the drafting frame. The condensing zone is here formed by a hollow member forming a suction device and whose outer contour is a sliding surface over which a transport belt is looped.
Another apparatus within the art of such drafting units is the double-belt drafting frame of German patent document DE 41 39 067 C2 which is provided for a spinning machine and in which the fiber bundling zone has a pair of belts which pass around a roller pair and in which the roving is fed directly into the supply roll pair.
In general, these fiber bundling or condensing (compaction) systems have been found to be effective and the use of condensing units or fiber bundling units for rovings on drafting frames has become relatively widespread.
It is however an object of the present invention to improve upon the prior art systems previously described and, in particular, to provide a drafting frame for a spinning machine in which the condensation of the roving which is effected in the fiber bundling zone can be made more effective in a simple manner.
Another object of this invention is to provide an improved fiber bundling system for a drafting frame for use in or in conjunction with a spinning machine.
These objects and others which will become apparent hereinafter are attained, in accordance with the invention, in a drafting frame for a spinning machine which comprises:
a succession of spaced-apart roller pairs operating at different peripheral speeds and drafting a roving between the roller pairs, the succession of roller pairs having an output roller pair with an upper roller and a lower roller delivering the roving from a first nip between them; and
a fiber bundling zone immediately downstream of the output roller pair for subjecting the delivered roving to suction for drawing fibers of the roving together, the fiber bundling zone being formed with:
a suction shoe juxtaposed with the roving and connected to a suction source,
a perforated transport element looped around the suction shoe and supporting the roving while suction applied through the transport element condenses the roving by drawing fibers of the roving together, and
an inclined belt converging toward the perforated transport element in a direction of travel of the roving through the fiber bundling zone and forming a second nip with the perforated transport element, the first and second nips delimiting upstream and downstream ends of the fiber bundling zone.
In other words the objects of the invention are achieved by providing the perforated transport medium in juxtaposition with a belt which converges toward the perforated transport medium to a second clamping location or nip. This belt provides a wedge action which has been found to improve the compaction or condensation of the roving in the region of the fiber bundling zone. The combination of the moving transport medium and the converging belt means that there are no stationary surfaces which can lead to uncontrolled fiber movements or, especially, to buckling. The roving and all of the fibers thereof are continuously displaced between the moving surfaces which prevent those uncontrolled movements and buckling. Optimum air flow conditions can be maintained as well and thus the consumption of air can be reduced.
In a drafting frame in which the second nip or the clamping location is defined by a perforated transport medium in the form of a lower belt toward which the upper belt converges, it is advantageous to provide the upper belt so that it runs toward the lower belt from a location upstream of the second nip and at which the height of the upper belt above the roving can be adjusted. This may be achieved by adjusting the member, here referred to as a rerouting element, about which the upper belt passes. The adjustability of this member allows the gap between the belts in the fiber-bundling zone to be optimally adjusted based upon the kind of staple fiber yarn which may be processed.
According to a feature of the invention, therefore, the perforated transport element is a lower belt passing around the suction shoe and a clamping roller located on a lower side of the second nip, the inclined belt being an upper belt passing around a rerouting element located at a distance from the lower belt at an upstream end of the zone and an upper clamping roller on an opposite side of the second nip.
The upper and lower belts form a wedge through which the roving passes and cleaning edge is provided downstream of the wedge. The lower belt can be looped around the cleaning edge.
Furthermore the lower roller can be located between the suction shoe and the cleaning edge.
According to another feature of the invention a drive roller bears upon the aforementioned lower roller for driving same.